1. Field of the Invention
The present invention relates to an optical apparatus, an exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
A semiconductor exposure apparatus transfers an original having various kinds of patterns onto a substrate, such as a silicon wafer. To generate an integrated circuit, it is indispensable to improve not only the resolution, but also, the overlay accuracy.
Overlay errors in the semiconductor exposure apparatus are classified into an alignment error, image blurring, and a magnification error. Adjusting the relative displacement between an original (reticle) and a substrate (wafer) makes it possible to reduce the alignment error. Moving some optical elements of an optical system makes it possible to eliminate the image blurring and magnification error. In moving the optical elements, it is necessary not to increase a parallel decentration error and an inclined decentration error.
A positive servo system moves and positions the optical elements. A laser interferometer attached to a lens barrel or a reference structure outside it measures the positions of the optical elements.
Along with the recent increase in the degree of micropatterning of semiconductor devices, it is being demanded that optical elements should have a higher position/attitude accuracy and a higher positioning accuracy to correct, e.g., aberration, as compared with the prior art, to obtain required imaging. Disturbance often degrades the positioning accuracy. The influence of the disturbance has been negligible under the conventional positioning control, but it is becoming non-negligible to meet the demand for a higher positioning accuracy. Japanese Patent Laid-Open No. 2005-236258 discloses an example in which positioning control of optical elements, such as a lens barrel, is performed on the basis of only position information obtained by measurement with reference to a support for supporting the optical elements. In this example, elastic deformation of the support causes a measurement error, to result in degradation in the positioning accuracy of the optical elements.